IB/hfi1: Add tx_opcode_stats like the opcode_stats

This patch adds tx_opcode_stats to parallel the
(rx)opcode_stats in the debugfs.

Reviewed-by: Kaike Wan <kaike.wan@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>